Smart Hybrid Nanocomposite for Photodynamic Inactivation of Cancer Cells with Selectivity

Biochemical Basis of Selective Accumulation and Targeted Delivery of Photosensitizers to Tumor Tissues

The method of photodynamic therapy for treatment of malignant neoplasms is based on the selective of accumulation of photosensitizers in the tumor tissue. Insufficient selectivity of photosensitizers in relation to pathologically altered tissues and generalized distribution throughout the body leads to the development of severe toxic effects, including skin phototoxicity. The mechanisms underlying selectivity of photosensitizers for tumor tissue include selective binding to blood proteins and lipoproteins (considering that the number of receptors for those is increased on tumor cell membranes), uptake by macrophages, better solubility at low pH (acidic pH is characteristic of tumor cells), and other mechanisms. At present, increase in the efficiency of photodynamic therapy is largely associated with the additional targeting of photosensitizers to tumor tissues. Targeted delivery strategies are based on the differences in metabolism and gene expression profiles between the tumor and healthy cells. There are differences in expression of receptors, proteases, or transmembrane transporters in these cells. In particular, accelerated metabolism in many types of tumors leads to overexpression of receptors for epidermal growth factor, folic acid, transferrin, and a number of other compounds. This review considers biochemical basis for the selective accumulation of various classes of photosensitizers in tumors (chlorins, phthalocyanines, 5-aminolevulinic acid derivatives, etc.) and discusses various strategies of targeted delivery with emphasis on conjugation of photosensitizers with the receptor ligands overexpressed in tumor cells.

Magnetically Boosted Generation of Intracellular Reactive Oxygen Species toward Magneto-Photodynamic Therapy

The generation of reactive oxygen species (ROS) in photodynamic therapy (PDT) involves excited-state intermediates with both singlet and triplet spin configurations, which provides possibilities to modulate the ROS production in PDT under an external magnetic field. Here, we present that magnetically modulated ROS production can promote PDT efficacy and develop a magnetic-field-assisted PDT (magneto-PDT) method for effectively and selectively killing cancer cells. The photosensitization reaction between excited-state riboflavin and oxygen molecules is influenced by the applied field, and the overall magnetic field effect (MFE) shows a moderate increase at a low field (<1000 G) and then a boost up to the saturation ∼100% at a high field (>1000 G). It is found that the spin precession occurring in radical ion pairs (electron transfer from riboflavin to oxygen) facilitates the O₂^•- generation at the low field. In comparison, the spin splitting in an encounter complex (energy transfer from riboflavin to oxygen) benefits the production of ¹O₂ species at the high field. The field modulation on the two types of ROS in PDT, i.e., O₂^•- and ¹O₂, is also demonstrated in living cells. The magneto-PDT strategy shows the capability to inhibit the proliferation of cancer cells (e.g., HeLa, RBL-2H3, and MCF-7) effectively and selectively, which reveals the potential of using the MFE on chemical reactions in biological applications.

Nanomaterials for Deep Tumor Treatment

According to statistics, cancer is the second leading cause of death in the world. Thus, it is important to solve this medical and social problem by developing new effective methods for cancer treatment. An alternative to more well-known approaches, such as radiotherapy and chemotherapy, is photodynamic therapy (PDT), which is limited to the shallow tissue penetration (< 1 cm) of visible light. Since the PDT process can be initiated in deep tissues by X-ray irradiation (X-ray induced PDT, or XPDT), it has a great potential to treat tumors in internal organs. The article discusses the principles of therapies. The main focus is on various nanoparticles used with or without photosensitizers, which allow the conversion of X-ray irradiation into UV-visible light. Much attention is given to the synthesis of nanoparticles and analysis of their characteristics, such as size and spectral features. The results of in vitro and in vivo experiments are also discussed.